ES2490818T3 - Waste filter for use in a nuclear fuel assembly - Google Patents

Abstract

Waste filter (6) for use in a nuclear fuel assembly (2), comprising a group of fuel rods (4) to which a flow of cooling fluid is to be supplied, of the type comprising a plurality of conduits flow (22) extending in a longitudinal direction (L), each one being delimited between a pair of walls (20), in which the filter (6) comprises baffles (24, 26, 28; 74) that protrude into the interior of each conduit (22) alternately from the pair of walls (20) overlapping in the longitudinal direction (L) to define a zigzag flow channel (30) and provided with at least one set of holes (36) aligned in the longitudinal direction (L) to define through the superimposed baffles (24, 26, 28; 74) a passage (38) to house a lower end stem (14) of a rod (4) of fuel.

Description

E08306029

08-08-2014

DESCRIPTION

Waste filter for use in a nuclear fuel assembly.

The present invention relates to a waste filter for use in a nuclear fuel assembly comprising a group of fuel rods to which a flow of refrigerant fluid is to be supplied, of the type comprising a plurality of flow ducts which extend in a longitudinal direction, each being delimited between a pair of walls.

A nuclear fuel assembly for a light water reactor conventionally comprises a group of elongated fuel rods that extend parallel to each other. In use, the fuel assembly is oriented vertically in a nuclear reactor core and a cooling fluid is flowed upward between the fuel rods.

15 There may be residues in the coolant and damage the fuel rods, therefore requiring removal or replacement of the damaged fuel assembly or fuel rods. In a known manner, a waste collector or filter is placed upstream of the group of fuel rods to trap waste.

EP 0 455 010 discloses a waste filter having a plurality of flow ducts

20 to allow the refrigerant fluid to flow up through the waste filter, the ducts being curved to trap waste.

An object of the invention is to provide a waste filter that allows improved entrapment of waste, namely waste in the form of flexible cables.

For this purpose, the invention proposes a waste filter for a nuclear fuel assembly of the type mentioned above, in which the filter comprises baffles protruding into each duct alternately from the pair of overlapping walls in the longitudinal direction to define a zigzag flow channel and provided with at least one set of holes aligned in the longitudinal direction to define through the

30 superimposed baffles one step to accommodate a lower end rod of a fuel rod.

In other embodiments, the waste filter comprises one or more of the following characteristics, taken separately or in any technically feasible combination:

35 - comprises in each conduit, aligned in the longitudinal direction with each passage, a cell to accommodate a lower end plug of a fuel rod;

- it comprises at least one spring provided in each cell to transversely and / or longitudinally support a lower end plug housed in the cell; 40 - comprises walls each composed of at least one metal sheet provided with at least one deflector fold to form a deflector;

- comprises intermediate walls that separate two adjacent ducts, each consisting of two metal sheets provided with deflector folds protruding on opposite sides of the wall;

- each intermediate wall is provided with a deflector fold protruding from one of the opposite faces of the wall at an intermediate level, with two deflector folds protruding from the other of the opposite faces of the wall;

50 - includes baffles formed by plates fixed to the walls at an angle;

- comprises intermediate walls that separate two adjacent ducts each provided with at least one baffle plate interlocked with the intermediate wall to form two baffles, each one protruding on a respective face of the wall;

- comprises at least a pair of adjacent intermediate walls provided with baffle plates that intersect the corresponding intermediate walls at the same level; Y

60 - includes connection bands interlocked perpendicularly with the walls.

The invention also relates to a nuclear fuel assembly comprising a group of fuel rods extending in a longitudinal direction, each comprising a rod at a lower end and a waste filter as defined above, the rod being of each fuel rod

65 housed in one step.

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In one embodiment, the nuclear fuel assembly comprises a grid-shaped support plate disposed below the waste filter, said support plate comprising bars defining openings therebetween, the bars being arranged to support the rods of fuel extending through the passages and the openings being arranged to allow refrigerant to flow through the support plate

5 inside the filter channels.

The invention and its advantages will be better understood by reading the following description provided by way of example only and with reference to the accompanying drawings, in which:

10 - Figure 1 is a partial sectional view of a lower end part of a nuclear fuel assembly illustrating a waste filter of the nuclear fuel assembly;

Figure 2 is an enlarged view of the lower end portion of the nuclear fuel assembly of Figure 1; 15-Figures 3 and 4 are partial perspective views, exploded in order and assembled respectively, of the waste filter of Figure 1; Y

Figures 5 to 8 are views similar to those of Figures 1 to 4, which illustrate another embodiment of a waste filter.

The nuclear fuel assembly 2 of Figure 1 comprises a group of fuel rods 4, a waste filter 6 for filtering waste contained in a refrigerant fluid supplied to the group of fuel rods 4 and a support plate 8 to support the filter 6 and the fuel rods 4.

25 The fuel rods 4 are elongated and extend parallel to each other in a longitudinal direction L. The fuel rods 4 are arranged in a crosshair (for example, a 10x10 crosshair) and transversely separated to allow a flow of coolant fluid between them mainly in the longitudinal direction L.

In use, the fuel assembly 2 is placed in a nuclear reactor core with the substantially vertical longitudinal direction L and a cooling fluid is supplied to flow mainly upward in the longitudinal direction L as illustrated by the arrow F in Figure 1. Next, the terms related to the orientation refer to the position of the fuel assembly 2 as used in a

35 nuclear reactor core.

Each fuel rod 4 comprises a tubular liner 10 to accommodate a stack of nuclear fuel pellets (not shown), a lower end plug 12 to close the lower end of the liner 10 and a lower stem 14 protruding downwardly from the cap 12 with a lower end and a diameter smaller than

40 lower end plug 12. Only the lower end parts of four fuel rods 4 are visible in Figure 1.

The filter 6 is arranged at the lower end of the group of fuel rods 4 and extends transversely. It comprises a lower face 16 and an upper face 18.

The filter 6 comprises walls 20 distributed in a first transverse direction T1 in separate relation to a constant spacing P (Figure 2), each pair of adjacent walls 20 defining between them a conduit 22 that allows the cooling fluid to flow upwards to through filter 6.

50 The walls 20 are elongated and extend parallel to each other in a second transverse direction T2 (Figure 3) perpendicular to the first transverse direction T1 (ie, perpendicular to the plane of Figure 1)

As illustrated in Figure 2, each wall 20 is provided with baffles 24, 26, 28 protruding from the wall 20 transversely to each adjacent wall 20.

55 The baffles 24, 26, 28 projecting in each duct 22 of the pair of adjacent adjacent walls 20 defining the duct 22 are interwoven with overlap in the longitudinal direction L to define within the duct 22 a zigzag flow channel 30.

The term "zigzag" refers, in the context of the invention in a general way, to a non-linear channel which has successive sections inclined in relation to the longitudinal direction L and which extends alternately from a wall of the pair from walls to the other wall (in figure 2 from right to left and from left to right).

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The baffles 24, 26, 28 projecting in each duct 22 are alternated along the longitudinal direction L between a baffle of a wall 20 and a baffle of the other wall 20 of the pair of adjacent and facing walls 20 that define the duct 22

Each intermediate wall 20 separating two adjacent ducts 22 is provided with an upper baffle 24 and a lower baffle 26 protruding on one side of the wall 20 with a longitudinal separation therebetween, and an intermediate baffle 28 protruding on the opposite face. of the wall 20, at an intermediate level of the upper and lower baffles 24, 26.

The walls 20 that delimit a single conduit 22 comprise either a lower baffle 26 and an upper baffle 24 or an intermediate baffle 28, as illustrated to the right and to the left in Figure 1. Such walls 20 are provided, by for example, at the ends of the filter 6 or adjacent openings for water channels in case a filter is used in a BWR fuel assembly (boiling water reactor).

Back to Figure 2, the spacing P is fixed so that each intermediate baffle 28 of a wall 20 is inserted between the upper and lower baffles 24, 26 of an adjacent dividing wall 20 with overlap in the longitudinal direction L.

The baffles 24, 26, 28 protruding in each duct 22 are longitudinally separated so that the width W of the channel 30 (defined as the distance between facing faces of the baffles 24, 26, 28 defining a channel 30) is smaller than the spacing P.

Each channel 30 comprises two inclined sections 32, 34 which extend at an angle in relation to the longitudinal direction L. The channel 30 comprises a lower inclined section 32 which extends upwardly and laterally on a first side (to the left in the Figure 2) from the lower face 16 and an upper inclined section 34 extending upwardly and laterally on the opposite side (to the right in Figure 2) from the lower inclined section 32.

The lower inclined section 32 of each channel 30 is defined between a lower deflector 26 and an intermediate deflector 28 of a pair of adjacent walls 20, and its upper inclined section 34 is defined between an intermediate deflector 28 and an upper deflector 24 of the pair of adjacent walls 20.

In each conduit 22, the superimposed baffles 24, 26, 28 are provided with sets of holes 36 aligned along a longitudinal axis A to define through the superimposed baffles 24, 26, 28 steps 38, each to accommodate the stem 14 of a respective fuel rod 4. Each set of aligned holes 36 defines a step 38.

The passages 38 are distributed in the conduits 22 of the filter 6 correspondingly with the fuel rods 4. Specifically, the aligned hole assemblies 36 are distributed in the superimposed baffles 24, 26, 28 in each conduit 22 along the second transverse direction T2.

The diameter of the holes 36 is adapted so that the stems 14 are accommodated with a clearance in the holes 36 in relation to the axis A of step 38. Therefore, an annular flow path is defined around each stem 14.

Each inclined section 32, 34 of each channel 30 cuts the steps 38 that extend through the baffles 24, 26, 28 defining the channel 30. Therefore, each channel 30 cuts the corresponding steps 38 twice.

Each intermediate wall 20 separating two adjacent ducts 22 is composed of two metal sheets 40, 42 fixed to each other, the baffles 24, 26, 28 of the dividing wall 20 being composed of folds of the sheets 40, 42. Each wall 20 of This type comprises a hollow cavity 44 delimited between the folds of the two sheets 40, 42.

Each end wall 20 that delimits a single conduit 22 is composed of a metal sheet or two metal sheets, one of which is provided with at least one deflector fold.

As illustrated in Figures 3 and 4, the filter 6 comprises connection bands 46 interwoven at 90 ° with the walls 20 and which give the filter 6 a cross-linked or grid-shaped structure.

The connecting bands 46 and the walls 20 are provided with opposite grooves 48 (Figure 3) of their edges to interlock the bands 46 with the walls 20.

The walls 20 comprise upper portions 50 that extend upwardly from the baffles 24, 26, 28. The upper portions 50 define with the connection bands 46 a reticule of square cells 52 (Figure 4). Each cell 52 is aligned with a respective passage 38 and adapted to accommodate the lower end plug 12 of a respective fuel rod 4.

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The upper part 50 of the walls 20 and the connecting bands 46 are provided with springs 54, 56, respectively, to transversely support the lower end caps 12 housed in the cells 52 and prevent a lifting of the fuel rods 4.

The springs 54, 56 are trimmed on the faces of each cell 52 defined by the dividing walls 20 and the connecting bands 46. A spring 54, 56 is provided on each face of the cell 52.

Preferably, each cell 52 is provided with at least two springs in order to fix the fuel rods 4 against unwanted vertical movements, partial length BWR fuel rods included. In an alternative embodiment, each cell 52 is provided with a single annular spring assembled on the walls 20 and / or connecting bands 46.

As illustrated in Figure 4, the lower end caps 12 of the fuel rods 4 are provided with annular notches 57 and the springs 54, 56 are adapted to extend into the notches 57.

Each connection band 46 extends downward towards the lower edge of the walls 20. Thus, the connection bands 46 subdivide each channel 30 between each step 38. To allow insertions of the connection bands 46, the baffles 24, 26, 28 of each wall 20 are provided with openings 58 (Figure 3) located between the holes 36.

As illustrated in Figure 1, the support plate 8 is arranged below the filter 6. It has a grid shape and comprises bars 60 defining openings 62 therebetween.

The bars 60 of the support plate 8 extend aligned with the steps 38 and the stems 14 extend through the steps 38. The bars 60 provide an axial stop to the stems 14 of the fuel rods 4 and are designed to carrying the load of the fuel rods 4, whereby the support plate 8 supports the fuel rods 4.

As illustrated in Figure 2, the passages 38 and the channels 30 are configured so that the cooling fluid supplied through the openings 62 of the support plate 8 to the lower face 16 of the filter 6 flows into the interiors of the channels 30 (arrow F1) and the annular flow paths defined within steps 38 around stems 14 (arrows F2).

Preferably, the dimensions are chosen such that the flow resistance of the channels 30 and that of the annular flow paths are comparable, taking into account the zigzag shape of the channels 30, the width W of the channels 30, the obstruction partial provided by the stems 14 in the channels 30 depending on the diameter of the stems 14, and the clearance between the holes 36 and the stems 14.

In one example, the rod diameter is approximately 3.5 mm, the diameter of the holes 36 is approximately 6.5 mm, the radial clearance of approximately 1.5 mm, the width W of the channels 30 is approximately 2.8 mm and the P spacing is approximately 12.65 mm.

In use, the refrigerant fluid is supplied to the lower face 16 of the filter 6 and flows mainly upward in the longitudinal direction L, as illustrated by arrow F in Figure 1. The refrigerant fluid flows in each conduit 22 entering channel 30 (arrow F1) and the annular flow paths (arrow F2) defined in each step 38 around the stems 14.

The deviated shape of the channels 30 allows to trap waste.

The current flowing through each annular flow path interferes with the current flowing through the corresponding channel 30. This avoids imparting any preferred orientation to the residues within the channel 30 and allows improved waste retention.

The stems 14 that extend into each channel 30 form obstacles that impair the flow of fluid in the channel 30 and prevent a clear orientation of the waste.

The fuel rods 4 are fixed against a lateral shaking and a longitudinal lifting by the springs 54, 56 provided in each cell 52 defined by the upper parts 50 of the dividing walls 20 and the connecting bands 46 above the channels 30.

The anti-lifting function is improved by the notch 57 to accommodate the springs 54, 56 while a simple insertion of the fuel rods 4 is allowed when the fuel assembly 2 is assembled.

The stems 14 of the fuel rods 4 that are housed in the steps 38 provided in the filter 6 also contribute to fixing the fuel rods against lateral shaking and longitudinal lifting.

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The cavities 44 defined between the bent baffles 24, 26, 28 of the sheets 40, 42 also allow to trap debris.

5 The connecting bands 46 that subdivide each channel 30 improve the entrapment of elongated debris oriented in the second transverse direction T2.

The filtering function and the support function are operated by the same structure (filter 6) which has a reduced height. The height of the rod 14 can normally be approximately 15 mm.

10 Since the waste filter 6 also fixes the fuel rods 4, it is possible to suppress the first conventional space grid located at a distance above the lower end waste filter 6, thus saving on costs.

The filter 6 arranged on the support plate 8 and adapted to accommodate the lower end part of the fuel rods 4 allows to provide fuel rods 4 with an additional length that could serve as a fission gas chamber and / or to increase the total amount of fissile material in set 2.

Each wall 20 is obtained by initially providing flat sheets 40, 42 perforated with series of holes 36,

20 subsequently folding the sheets 40, 42 to define the baffles 24, 26, 28 and fixing the sheets 40, 42 with each other. In the flat state, the sheets 40, 42 provided with a single fold have a lower height than the sheets 40, 42 provided with two folds.

The embodiment illustrated in Figure 5 differs from that in Figures 1 to 4, in particular by the structure of the walls that delimit the ducts and the baffles.

In this embodiment, each wall 20 extends parallel to the longitudinal direction L and is provided with two interlocking baffle plates 72 forming an angle in relation to the wall 20 so that each baffle plate 72 defines two baffles 74 ( Figure 6) protruding on each side of the wall 20. The two plates of

30 deflector 72 are parallel and are longitudinally separated.

As illustrated in Figure 6, the baffle plates 72 intersect the walls 20 at an angle of less than 90 ° so that each baffle plate 72 defines a baffle 74 that extends upward on one side of the wall 20 (a right in figure 6) and a baffle 74 extending downward on the opposite side of the wall

35 20 (on the left in Figure 6).

In each duct 22, the downward deflectors 74 provided in a wall 20 of the pair of adjacent walls 20 that delimit the duct 22 are interwoven and overlap in the longitudinal direction L with the upward deflectors 74 provided in the another wall 20 of the pair of adjacent walls 20.

40 Thus, each channel 30 defined between two adjacent walls 20 has a zigzag shape and comprises three inclined sections that include an intermediate section that extends downward.

The baffles 74 are provided with assemblies of holes 76 aligned along the longitudinal axis A to define 45 steps 38 to accommodate the stems 14.

As illustrated in Figure 7, the filter 6 of the second embodiment has connection bands 46 of smaller height than the walls 20. They are interlocked on the upper edges of the walls 20 and terminate before the baffles 74.

50 The upper parts 50 of the walls 20 and the connecting strips 46 are provided with springs 54, 56 for laterally supporting lower end plugs 12 housed in cells 52 defined in between and preventing lifting of the fuel rods 4. In order to provide springs 54, 56 on each side of the walls 20 or in the connecting bands 46, they are formed, for example, of two sheets.

55 The walls 20 and the baffle plates 72 are provided with facing interlocking grooves 78 that extend halfway in length in the second transverse direction T2.

Each baffle plate 72 is provided with two parallel series of holes 76, each extending on a side 60 of the baffle plate 72 defining a baffle 74, that is on each side of the interlocking slot 78.

The length of the walls 20, plates 72, interlocking grooves 78 and the number of holes 76 are limited in Figure 7 for reasons of clarity and correspond, in practice, to the number of fuel rods 4 in the reticle. 65

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The filter 6 further comprises additional connection bands 80 interlocked on the lower edges of the walls 20 through facing interlocking grooves 82 provided on the lower edges of the walls 20 and the upper edges of the additional connection bands 80.

5 Filter 6 of Figures 5 to 8 offers the same advantages as that of Figures 1 to 4 with respect to trapping debris, except that the walls 20 lack internal cavities.

The filter 6 of Figures 5 to 8 can be obtained in a simple way, at low cost and with good reproducibility from essentially flat metal sheets.

10 The sections of the channels of the embodiments of Figures 1 to 4 and 5 to 8 are inclined at an angle less than or greater than 90 ° in relation to the longitudinal direction L. Alternatively, at least one section

or each section of a channel forms an angle of 90 ° in relation to the longitudinal direction L. This can be obtained in a variant of the filter of Figures 5 to 8 providing deflectors in the walls of each pair of walls

15 adjacent arranged at an angle of 90 ° in relation to the longitudinal direction L and with a displacement in the longitudinal direction L.

The number of channel sections of the embodiments of Figures 1 to 4 and Figures 5 to 8 is not limited to two or three. Alternatively or optionally, at least one or each channel has a different number of

20 sections, specifically two sections, three sections or more than four sections.

In the embodiments of Figures 1 to 4 and Figures 5 to 8, the walls 20 extend upward from the deflectors 24, 26, 28; 74. This makes it possible to define cells 52 to accommodate the lower end caps 12 and provide springs 54, 56 to laterally support said lower end caps 12.

In a variant, the dividing walls lack such springs and in such a case, the upper parts of the dividing walls may be shorter above the deflector to limit the height of the manifold while interlocking with connecting bands is allowed.

In the embodiments of Figures 1 to 4 and 5 to 8, the filter is disposed on the support plate and the fuel rods extend through the filter and abut the bars of the support plate. The filter may be arranged below the support plate. In such a case, holes can be omitted to define steps to accommodate the lower end portions of the fuel rods and / or the upper parts of the walls that extend above the baffles. In addition, the bars of the support plate are arranged to

35 support the lower end portions of the fuel rods and openings of the support plate are arranged to allow the refrigerant to flow out from the filter channels. Optionally, an additional space grid corresponding to the upper parts of the walls can be added on the support plate to provide lateral support to the lower end parts of the fuel rods.

40 Filters such as those in Figures 1 to 4 and 5 to 8 but lacking steps for the fuel rods and / or springs for a lateral support of the fuel rods still have the advantage of a simple and cheap construction.

The filters of Figures 1 to 4 and 5 to 8 are described for reasons of clarity for a reticule of fuel rods.

In a known manner, a pressurized water reactor (PWR) fuel assembly comprises guide tubes for housing rods in groups and may comprise an instrumentation tube for housing the core instrumentation. Such tubes that replace some of the fuel rods in the reticle do not comprise material

50 fissile and the filter is adapted to provide specific positions to accommodate the tubes.

A fuel assembly for a BWR conventionally comprises at least one water channel that replaces one or more fuel rods in the fuel rod reticule and the filter is adapted to allow such water channel to pass through the filter as in grids. spacers distributed along the rods of

55 fuel

The filter of the invention can be used for a fuel assembly of various types, such as fuel assemblies for use in BWR (boiling water reactor) or PWR (pressure water reactor).

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Claims (10)

E08306029 08-08-2014 1. Waste filter (6) for use in a set (2) of nuclear fuel, comprising a group of fuel rods (4) to which a flow of refrigerant fluid is to be supplied, of the type comprising a 5 plurality of flow ducts (22) extending in a longitudinal direction (L), each being bounded between a pair of walls (20), wherein the filter (6) comprises baffles (24, 26, 28; 74) that protrude into each duct (22) alternately from the pair of walls (20) with overlap in the longitudinal direction (L) to define a 10 channel (30) of zigzag flow and provided with at least one set of holes (36) aligned in the longitudinal direction (L) to define through the superimposed baffles (24, 26, 28; 74) a passage (38 ) to accommodate a lower end rod (14) of a fuel rod (4). 2. Waste filter according to claim 1, comprising in each duct (22), aligned in the direction Longitudinally (L) with each passage (38), a cell (52) to accommodate a lower end plug (12) of a fuel rod (4). 3. Waste filter according to claim 2, comprising at least one spring (54, 56) provided in each cell

(52)

to support transverse and / or longitudinally a lower end plug (12) housed in the cell (52). twenty

4. Waste filter according to any of the preceding claims, comprising walls (20), each of which is composed of at least one metal sheet (40, 42) provided with at least one deflector fold to form a deflector ( 24, 26, 28).

5. A waste filter according to claim 4, comprising intermediate walls (20) separating two adjacent ducts (22), each consisting of two metal sheets (40, 42) provided with protruding deflector folds. on opposite sides of the wall (20).

6. Waste filter according to claim 5, wherein each intermediate wall (20) is provided with a fold of 30 baffle protruding from one of the opposite faces of the wall (20) at an intermediate level, with two deflector folds protruding from the other of the opposite faces of the wall (20). 7. Waste filter according to any of the preceding claims, comprising baffles (74) formed by plates (72) fixed to the walls (20) forming an angle. 35 8. Waste filter according to claim 7, comprising intermediate walls (20) separating two adjacent ducts (22), each of which is provided with at least one deflector plate (72) interlocked with the wall (20) intermediate to form two baffles (74), each protruding on a respective face of the wall (20). 40 9. Waste filter according to claim 8, comprising at least one pair of adjacent intermediate walls (20) provided with baffle plates (72) intersecting the corresponding intermediate walls (20) at the same level. A waste filter according to any one of the preceding claims, comprising connection bands (46, 80) interlocked perpendicularly with the walls (20). 11. Nuclear fuel assembly (2), comprising a group of fuel rods (4) extending in a longitudinal direction (L), each comprising a rod (14) at a lower end and a filter (6) from 50 waste according to any one of the preceding claims 1 to 10, the rod (14) of each fuel rod (4) being housed in a passage (38). 12. Nuclear fuel assembly (2) according to claim 11, comprising a shaped support plate of grid (8) arranged below the waste filter (6), said support plate (8) comprising bars 55 (60) defining openings (62) therebetween, the bars (60) being arranged to support the rods (4) of fuel extending through the passages (38) and the openings (62) being arranged to allow refrigerant to flow through the support plate (8) into the channels (30) of the filter ( 6). 8